Display apparatus

ABSTRACT

A display apparatus which utilizes a display device having an arrangement of a plurality of figure points with a predetermined interval therebetween and the emit lights of each of the figure points are individually controllable. According to the present invention, such a display apparatus provides a diffraction screen which provides diffraction holes for passing lights emitted from selected figure points and said diffraction holes diffract the image of said selected figure points. The image of said selected figure points and the diffracted image of said selected figure points are combined and displayed.

[ Oct. 21, 1975 Kiemle et al. ABSTRACT 4 Claims, 6 Drawing Figures Primary ExaminerDavid L. Trafton Attorney, Agent, or FirmAllan Ratner A display apparatus which utilizes a display device having an arrangement of a plurality of figure points with a predetermined interval therebetween and the emit lights of each of the figure points are individually controllable. According to the present invention, such a display apparatus provides a diffraction screen which provides diffraction holes for passing lights emitted from selected figure points and said diffraction holes diffract the image of said selected figure points. The image of said selected figure points and the diffracted image of said selected figure points are combined and displayed.

DISPLAY APPARATUS Ishizaki, Akashi; Keizo Kurahashi, Kobe, all of Japan Assignee: Fujitsu Limited, Japan Filed: Jan. 4, 1974 [21] Appl. No.: 430,628

Foreign Application Priority Data Jan. 11, 1973 48-6479 340/366 B; 340/324 M; 340/378 A; 350/162 R; 350/162 SF Int. G08B 5/36 Field of Search................... 350/162 R, 162 SF; 340/366 B, 378 A References Cited UNITED STATES PATENTS United States Patent Murase et al.

[75] Inventors: Kenji Murase, Kakogawa; Hiroyuki [52] US. Cl.....

U.S. Patent Oct.21, 1975 Sheet 1 of3 3,914,761

US. Patent Oct. 21, 1975 Sheet2of3 3,914,761

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U.S. Patent Oct. 21, 1975 Sheet 3 of3 3,914,761

DISPLAY APPARATUS BACKGROUND OF THE INVENTION The present invention relates to a display apparatus which utilizes a dot pattern type display device and, especially, to an improvement of the quality of the figures which are displayed on said display device.

A plasma display panel, a liquid crystal display device, an electroluminescent display device and an LED display device which utilizes light emitting diodes are well known as dot pattern type display devices with matrix form. These display devices have flat panel forms and recently have been used in the terminal installation for information processing systems, because said display device is very small in depth and can be driven by digital control signals.

However, in such a display device, the displayed information is presented by the dot pattern being composed of a plurality of selected figure points and no information is presented between said figure points.

Therefore, the information displayed on the abovementioned display devices is discontinuous and the fineness of the displayed information is more spoiled than in the cathode ray tube display device. This discontinuousness is more clearly apparent in a picture display having halftones than in a character display.

In one prior technique for displaying the picture on a plasma display panel, each picture element is composed of a plurality of figure points which are arranged in adjacent positions and the predetermined weight of brightness is given to each figure point of the every pic ture element. Brightness modulation is carried out by selecting a combination of the above-mentioned figure points and the picture is displayed by the selected combination of the figure points in each picture element. Actually, the displayed picture information has an uncertain outline and unclear display pattern, because said picture element is composed of the combination of the discontinuous dot pattern figure points.

SUMMARY OF PRESENT INVENTION The object of the present invention is to improve the quality of the figures displayed on a dot pattern type display device. More specifically, the object of the present invention is to provide a display apparatus which comprises a dot pattern type display panel or device such as a plasma display panel, and which can display characters, figures or pictures with fineness and high quality.

The characteristic feature of the display apparatus of the present invention is to provide a diffraction screen which provides diffraction openings or holes in combination with a dot pattern type display panel or device and said diffraction screen diffracts the dot pattern image on said display device. The dot pattern image on said display device and the diffracted image by means of the-diffraction screen are combined and displayed.

Further features and advantages of the present invention will be apparent from the ensuing description with reference to the accompanying drawings to which, however, the scope of the invention is in no way limited.

BRIEF EXPLANATION OF THE DRAWINGS FIG. 1 is a sketch of one embodiment of the display apparatus according to the present invention;

FIG. 2 is one example of the diffraction screen which is utilizedfor explaining the principle of diffraction;

FIG. 3 is a diagram showing the distribution of the relative brightness in the X axis of the diffracted image by the diffraction screen shown in FIG. 2;

FIG. 4 is a diagram showing the distribution of the diffracted image by the diffraction screen shown in FIG. 2;

FIG. 5 is an arrangement of picture elements on the display panel which is composed of a plurality of figure points to each of which a brightness level is assigned;

' FIG. 6 is a diagram showing a combined image which is a combination of the displayed image and the diffracted image.

DETAILED EXPLANATION OF THE INVENTION Referring to FIG. 1, a display apparatus according to the present invention is composed of a plasma display panel 10 and a diffraction screen 20. The plasma display panel 10 is well known as a display device providing a memory function. The plasma display panel 10 is composed of, as shown in US. Pat. Nos. 3,559,190 and 3,499,167, a first glass base plate which provides a plurality of row electrodes covered with a dielectric layer and a second glass base plate which provides a plurality of column electrodes covered with a dielectric layer these plates being positioned to face each other and sandwich the gap filled with ionizable gas. A plurality of discharge points are formed at the portion where the row electrodes and the column electrodes cross through the gap filled with ionizable gas. The discharge points are fired selectively in accordance with figure points 11.

In FIG. 1, the plasma display panel 10 having a plurality of figure points 1 l is fixed to a front panel 12, and the row and column electrodes are connected via a flexible cable to a driving unit 13. Three supporting units 14a, 14b and 14c are provided on the front panel 12 and the length of the supporting units 14a, 14b and 14c can be adjusted. The top portions of the supporting units 14a 14b and respectively provide idle gears 15a, 15b and 156 and sliding guide members 16 a, 16b and 16c. One idle gear l5c is connected to a knob 17.

The diffraction screen 20 is composed of diffraction lattice 22 which is pulled in horizontal and vertical directions in the open portion of a circle frame 21. The circle frame 21 provides cogs which are formed on its peripheral surface and the cogs are geared with three idle gears 15a, 15b and 15c. Therefore, the circle frame 21 is supported by three sliding members 16a, 16b and 160. The angle of diffraction screen 20 which is provided in front of the plasma display panel can be changed by adjusting the angle of the knob 17, and the position of the diffraction panel can be determined by adjusting the length of supporting units 14a, 14b and 140.

FIG: 2 shows one example of the diffraction screen having the form of a lattice. In FIG. 2, each diffraction opening or hole provided in the diffraction screen has a square form. When a width 2a of each diffraction hole is a half of the picth l of the diffraction holes as shown in FIG. 2, the distribution of the intensity of the diffracted image becomes as shown in FIG. 3. In FIG. 3, the brightness of the direct image when the light source is placed facing the hole A, shown in FIG. 2, is shown by a relative brightness 1, and the brightness of the diffracted image is shown by the relative brightness with respected to the direct image. In FIG. 3, only the relative brightness in the X directin is shown, and the same diffracted image is obtained in the Y direction.

When we observe one small light source via the diffraction screen as shown in FIG. 2, a diffracted image which has a distribution of brightness as shown in FIG. 4 can be obtained. As shown in FIG. 4, the amount brightness in the X direction and the Y direction are combined. That is, four diffracted image points respectively having a relative brightness 0.4, shown by double circles, and eight diffracted image points respectively having a relative brightness 0.1 or 0.16, shown by broken circles, appear around the direct image having a relative brightness of 1.

Therefore, as shown in FIG. 1, by providing a diffraction screen 20 in front of a plasma display panel 10, the above-mentioned diffracted image points can fill up the space between figure points which are displayed on the panel 10. Accordingly, the displayed figure which is observed through the diffraction screen 20 appears to be a continuous pattern in spite of the dot pattern image of said displayed figure.

When a picture is displayed by the plasma display panel 10, a weight of brightness is assigned to every figure point according to a predetermined ratio as shown in FIG. 5. One picture element P is composed of four adjacent figure points (discharge points) and the levels of brightness are assigned to the four figure points included in each picture element F with the weight ratio of l, 2, 4 and 8 as shown in FIG. 5. An assignment of the brightness levels can be realized, by a well known method, such as by changing the frequency of the sustaining voltage for each figure point or by combining light absorbing plates. In the arrangement of the figure points as shown in FIG. 5, sixteen degrees of brightness information can be obtained by selecting a combination of the figure points which radiate in every picture element P.

However, in the above-mentioned method for displaying a picture with the figure points having the weight of the brightness, the recognition of the picture element cannot be carried out satisfactorily, because said picture element is composed of the figure points which emit light and discontinuousness is clearly apparent. For example, when we assume that the brightness level of the picture element shown in FIG. 5 surrounded by broken line P is eight (8), only the figure point which is hatched and has a brightness level of 8 emits light. Accordingly, a center of the picture element shown in FIG. does not coincide with the center of the picture element which is actually recognized.

Therefore, the displayed figure lacks clearness.

According to the present invention, such inconvenience can be avoided by utilizing the diffraction screen shown in FIG. 2.; That is, the quality of the displayed figure can be improved by superimposing the diffracted image by the diffraction screen and the displayed figure on the plasma display panel. When we arrange the diffraction screen with respect to the arrangement of the figure point as shown in FIG. 5, so that the figure point which has a brightness level 1 and which is positioned opposite, the figure point having a brightness level 8 is superimposed on the diffracted image point having a relative brightness level 0.4, and the center 0' of the radiation can approach the center 0 of the picture element P as shown in FIG. 6.

FIG. 6 shows the arrangement of the dot pattern which is obtained by the above-mentioned method. As shown in FIG. 6, the diffracted image points having the relative brightness 0.4, shown by a double circle, appear in the position of the figure point having the brightness level 1, which is adjacent to the position of the figure point having the brightness level 8. Therefore, the center of the brightness of the picture element P appears at displaced point 0' which is near the center point 0. For superimposing such a diffracted image on the direct displayed image, the axes X and Y of the arrangement of the diffraction holes of the diffraction screen should be placed inclined at 45 with respect to the axes X and Y of the arrangement of the figure points of the plasma display panel.

The adjustment of the axes X; and Y of the diffraction screen is carried out by turning the knob 17 shown in FIG. 1. When the character is displayed, the axes X and Y of the diffraction screen are preferably parallel respective to the axes X and Y of the plasma display panel. However, when the picture is displayed by the above-mentioned method, it is very effective to have the axes X and Y of the diffraction screen placed inclined with respect to the axes X and Y of the plasma display panel. The pitch or size of the diffracted image points are changed in accordance with the distance between the diffraction screen and the plasma display panel. Therefore, it is preferable to adjust the distance between the diffraction screen and the plasma display panel by adjusting the supporting units 14a, 14b and so that the finest figure is obtained.

As mentioned above, the center of the brightness of the picture element can be moved to the center of the picture element and the quality of the displayed figure or picture can be improved. Based on experiments conducted by the Inventors, the clearness of the displayed picture could be considerably improved by providing the above-mentioned diffraction screen. This diffraction screen was realized by providing wires crossing at right angles to each other with tensile force in front of the plasma display panel, as shown in FIG. 1.

The above-mentioned explanation has been directed to only one embodiment of the present invention, however, various kinds of modifications of the described embodiment can be realized. For example, the same effect can be obtained from the diffraction screen by utilizing diffraction holes having a form other than a square. Also the diffraction screen mentioned above can be placed in front of the plasma display panel as well as behind the plasma display panel when the panel is transparent. In other words, it is only necessary that the diffraction screen be placed in the light path of the displayed figure.

After all, the characteristic feature of the present invention is to provide a diffraction screen for a display panel or device having a dot pattern, and this invention is applicable not only to figure display but also to character or other types of displays by using a suitable pattern for the diffraction screen.

What is claimed is:

l. A display apparatus comprising a. a display device having an arrangement of a plurality of figure points with a predetermined interval therebetween, the emit lights of said figure points being individually controllable, a picture element having a plurality of said figure points adjacent to each other, and

b. a diffraction screen having diffraction holes arranged at an angle with respect to the arrangement of said figure points of said display device so that the center of brightness of said picture element appears near the center of said picture element.

2. A display apparatus according to claim 1, wherein each said picture element comprises four figure points with brightness weight ratio of l, 2, 4 and 8, and said diffraction holes are arranged at an angle of 45with respect to the arrangement of said figure points.

3. A display apparatus according to claim 1, wherein 

1. A display apparatus comprising a. a display device having an arrangement of a plurality of figure points with a predetermined interval therebetween, the emit lights of said figure points being individually controllable, a picture element having a plurality of said figure points adjacent to each other, and b. a diffraction screen having diffraction holes arranged at an angle with respect to the arrangement of said figure points of said display device so that the center of brightness of said picture element appears near the center of said picture element.
 2. A display apparatus according to claim 1, wherein each said picture element comprises four figure points with brightness weight ratio of 1, 2, 4 and 8, and said diffraction holes are arranged at an angle of 45*with respect to the arrangement of said figure points.
 3. A display apparatus according to claim 1, wherein said diffraction screen is further provided with a first supporting means for supporting said diffraction screen so that the distance between said diffraction screen and said display device may be changed.
 4. A display apparatus according to claim 1, wherein said diffraction sCreen includes second supporting means for supporting said diffraction screen so that the angle between the arrangements of said diffraction holes on said diffraction screen and said figure points on said display device may be changed. 